1. Field of the Invention
The invention relates to a method of fabricating a microcircuit card including in particular a step of coating the microcircuit with a hardenable coating material, typically a resin. It relates more particularly to improving the spreading of the coating material before hardening. The method advantageously also improves the adhesion of a resin or glue used during the fabrication of a microcircuit card.
2. Description of the Prior Art
Adapting the surface state of an article to improve the adhesion of glue to it is known in the art. For example, it is known that the surface energy (which can be expressed in joules/m2) of a glue or resin can be matched to that of the surface on which the glue or resin is deposited to obtain good adhesion, which is conditioned by proper wetting of the support by the resin or glue concerned.
Generally speaking, it is known that wetting is improved if the surface is made rougher. In particular, treating a surface by means of a laser beam to change its surface state is known in the art. On the other hand, excessive wetting can lead to excessive spreading of the glue or resin beyond the required boundaries.
A general object of the invention is to employ surface treatment techniques and more particularly surface treatment by a laser beam to improve control of the spreading of a glue or resin in a given step of the fabrication of a microcircuit card, with the aim of improving the control of spreading and/or adhesion of a hardenable material, possibly a heat-activated material.
The invention provides a method of fabricating a card incorporating a microcircuit, the method including the steps of coating the microcircuit in a hardenable coating material, treating the surface of a support incorporated in the card to define thereon at least two areas which have different surface states and both of which extend beyond a predetermined location of the microcircuit and are substantially concentric with that location, and subsequently depositing the material in an area centered relative to that location so that the material engulfs the microcircuit and so that the spreading of the material is dependent on the shapes, dimensions and surface states of the aforementioned two areas.
For example, the treatment of the surface of a support can define at least two such areas of different roughness. One area is then the result of the surface treatment while the other can be an untreated surface having the original roughness of the support itself, which is generally smoother. The aforementioned treatment preferably employs a laser beam. A UV laser beam can be used, for example, whose high photonic energy breaks the covalent bonds of the polymer material at the surface without significantly heating the surface. This avoids deformation of the polymer material constituting the support. On the other hand, a YAG laser can be used to form an array of microcavities or microgrooves on the support, leading to a macroscopic increase in roughness over and above the effect of modifying the surface energy of the material by ablation of the surface layers.
The treatment enables the use of an adhesive to be dispensed with for certain operations, for example, for fixing a module at the required location on the card body. The plastics material support (the card) can be directly mechanically anchored in said microcavities by applying a heating tool to cause the plastics material of the card to flow into the microcavities of the treated area.
With regard to the main problem, namely that of controlling the spreading of the resin (in other words, confining it within required boundaries) during a given operation, a variant of the surface treatment can be used to define an annular groove around the location of the microcircuit to limit the spreading of the aforementioned material. The resin is therefore confined by capillary action within the area delimited by the groove, so stabilizing the mass of coating material on top of and all around the microcircuit. An annular groove of this kind can be formed on the surface of the connecting board and/or on the bottom of the cavity and at a particular distance from its perimeter.
The invention will be better understood and other advantages of the invention will become more clearly apparent in the light of the following description of several embodiments of the invention, which description is given by way of example only and with reference to the accompanying drawings.